1. Field of the Invention
The present invention relates to an optical communication module for a universal serial bus, and more particularly, to an optical communication module for connecting D+ and D− ports of one-side universal serial bus to D+ and D− ports of the other-side universal serial bus through optical fiber liens.
2. Description of the Related Art
A universal serial bus (USB) is a bus of a protocol used in data communication between a computer and a wide variety of computer peripheral devices, and is often used in view of high compatibility in data communication. Such a USB is composed of a Vcc power line of 5 V, a ground line, a D+ data line and a D− data line. In D+ and D− data signals loaded on the D+ and D− data lines, the signals are both at a logic ‘low’ state in a “single-end-zero” area and are of opposite logic states in the other area.
If a one-side USB is connected to the other-side USB using metal lines, an allowable communication distance becomes shorter and a transmission rate is reduced due to a line voltage drop. To solve these problems, optical communication interface modules for connecting universal serial buses through optical fiber lines have recently been developed.
Referring to FIG. 1, a conventional optical communication interface module for a USB is constructed such that D+ and D− data signals of the USB are transmitted and received through different optical fiber lines.
A D+ port 106 of a side “A” USB is connected to a first D+ control switch 101 and a D− port 116 of a side “A” USB is connected to a first D− control switch 111. Likewise, a D+ port 126 of a side “B” USB is connected to a second D+ control switch 121 and a D− port 136 of a side “B” USB is connected to a second D− control switch 131.
The first and second D+ control switches 101 and 121 allow the D+ data signals input through first and second D+ amplifiers 103 and 123 not to be fed back through the first and second D+ drivers 102 and 122. The first and second D+ drivers 102 and 122 drive light emitting devices (LEDs) 104 and 124 in response to corresponding electrical data signals D+A and D+B, to generate corresponding D+ optical data signals. The D+ optical data signals supplied from the LEDs 104 and 124 are input to photo diodes 125 and 105, respectively, through optical fiber lines OF1 and OF2. The first and second D+ amplifiers 103 and 123 amplify data signals supplied from the photo diodes 105 and 125 to apply the same to the D+ ports 106 and 126.
Likewise, the first and second D− control switches 111 and 131 allow the D− data signals input through first and second D− amplifiers 113 and 133 not to be fed back through the first and second D− drivers 112 and 132. The first and second D− drivers 112 and 132 drive light emitting devices (LEDs) 114 and 134 in response to corresponding electrical data signals D−A and D−B, to generate corresponding D− optical data signals. The D− optical data signals supplied from the LEDs 114 and 134 are input to photo diodes 135 and 115, respectively, through optical fiber lines OF3 and OF4. The first and second D− amplifiers 113 and 133 amplify data signals supplied from the photo diodes 115 and 135 to apply the same to the D− ports 116 and 136.
As described above, the conventional optical communication interface module for a USB is constructed such that D+ and D− data signals of the USB are transmitted and received through different optical fiber lines because there is a single-end-zero area in which two data signals are both at a logic ‘low’ state. Accordingly, although the two data signals are at opposite logic states in areas other than the single-end-zero area, they must be transmitted and received through different optical fiber lines, resulting in a necessity of excessively many optical fiber lines.